Senior Full‑Stack Engineer (Frontend Focus)

TestBox is a startup that is building the next‑generation infrastructure for software transactions, transforming how buyers and sellers interact. The company’s platform marries synthetic data, orchestration, and a product graph to create a fluid, data‑driven experience. In this role, the Senior Full‑Stack Engineer (Frontend Focus) will own the end‑to‑end development of our sophisticated UI, turning complex backend capabilities into intuitive, powerful user interfaces. You will lead the creation of a component library, state‑management strategy, and design system that serve as the foundation for all product experiences. Key responsibilities • Design, build, and ship rich, interactive user interfaces for our core authoring tools, including visual workflow creation, data management, and real‑time collaboration. • Develop reusable component libraries in React and Next.js, establish consistent design patterns, and create comprehensive documentation for engineers and designers. • Partner with backend engineers to translate APIs into seamless frontend experiences, ensuring robust integration and data flow across the stack. • Conduct usability studies, gather feedback from customers, and iterate on prototypes to deliver polished, user‑centric products. • Mentor junior frontend engineers, guide best practices in testing, performance optimization, and accessibility. Required skills • At least 5 years of professional frontend engineering experience with a strong portfolio of complex web applications. • Deep expertise in modern frontend frameworks (React, Next.js, TypeScript), as well as state‑management libraries (Redux, Zustand, or Recoil) and build tools (Webpack, Vite). • Proficiency with CSS‑in‑JS, component styling, and responsive design principles; experience with design‑system tooling (Storybook, Figma integration). • Strong understanding of REST and GraphQL APIs, and the ability to create robust data connectors between front and back ends. • Familiarity with data visualization libraries (D3.js, charting tools) and canvas‑based interfaces is a plus. • Excellent problem‑solving skills, a passion for clean code, and a track record of building maintainable, high‑performance applications. Ideal candidate The candidate is a product‑centric designer‑coder who thrives in cross‑functional collaboration. They value simplicity and elegance in UX, yet can translate that into scalable, robust code. Their portfolio demonstrates a history of creating complex, data‑intensive tools that empower non‑technical users. They enjoy mentorship, are comfortable speaking to both technical and non‑technical stakeholders, and possess a strong sense of ownership. Their experience with B2B SaaS and developer tools signals their ability to solve for technical audiences, making them a natural fit for TestBox’s ambitious platform.